Thermoadhesive composition and composite closure liner formed therewith



Patented May 20, 1952 UNITED sr res NT FIEE THERMOADHESIVE COMPOSITION AND THEREWITH COMPOSITE CLOSURE LINER ew York' No Drawing. Application May 8,1946,

Serial No. 668,310

(o1. ze -28.5)

2 Claims. 1

It has been a practice in making closures havingtcushioned liners; .for example, in crown seals for-bottles, etc., to have a cork cushion-cemented totthemetal shell, and the bottle, etc., orifice is closediby a liner or spot which is secured to the cushion by a gutta percha cement.

According to. the present invention, a superior article is produced by securing the spot to the cushion. by acement consisting essentially of a mixture of. butylrubber and parafiin; the characteristics of such mixture giving benefit to it use under conditions of, hot application and under conditions where a strong and self-healing cement film is desired for; making such closure linerstand inother cases ,Where repeated transition from tacky adhesiveness to non-tacky adherence is desired.

Butyl rubber is an article of commerce, being produced in known ways from petroleum hydrocarbons bylQW-temperature catalytic polymerizing,,-combinations of isobutylene with butadiene or,.preferab1y, isoprene, and having characteristicseresemblingthose of natural rubber but differingtherefrom in its behavior in the presence of-petroleumoils and Waxes or more facile mixing and therfi hibition Q -Superior conditions of ades ven s wh n admi d th As arr-example of practice, 10 pounds of commercial :butyl-rubber (GR-L60) was mixed, on a rubber: mi l at ro temp ratur With 10 p u of ordinary paraifin; wax until a uniform product esu s-H Thismahrial. was, h a to a ut 250 degrees F., becoming quite fluid, and was applied to a base consisting of aluminum foil oi the grade thickness employed for crown seal spots, and was -spread; and worked into a film having a thickness of about 0,002 to 0.003 inch, and then cooled to;fix it in place. Hot roller coating or doctor blade apparatus can be used: for small surf-aces, a plate or spatula can be employed. The mixture is-plastic and adherent to the sheet at 200; degrees E. and will harden to increased strength and-tightly adherent condition when t t t-10.0 i9 29- cgr e Q below, o h the coated iilm can then be handled and is essentially free oi tackiness at normal room temperatures.

When h ba e. a i s wa n is not to be mediately used, as is the normalcase in placing spots in crown seals, it is preferable to roll the cooled composite into a coil for storage and shipment, When the material is compounded for a very low softening or tacky temperature, a glassine or cloth inter-leaf may be used. The spotting machine then receives such a roll and unwinds it, While strippingthe interleaf away if r 2 t such be used, and advancing the laminar web of 1 nd b at n .ihrei h e d o P n hing the spots andapplying-them to the cushions of the crown seals under heated conditions whereby he a d mi t res es e adp a and thereby adherent to the-cushions.

The f usion, tacky, and hardening temperatures for the mixture can bedcontrolled by proportioning. Thus, a desirable and eiiective range of properties can be attained by relative proportions by weight of butyl rubber parafiin wax of substantially 5025 0 to 60:40 qontents of butyl rubher much less than 50 percent are usually too low in tensile strength andhardening temperature to permit easy employment in the spottin machines, due to premature softening and. tackiness under the hotconditions of operating the machines, and also have a reduced adhesiveness: while a content of '70; percent or over of butyl rubber leads to mixt ures which do not exhibit the necessary tackiness, adhesiveness and thermoplasticity to provide adequate ementing layers. Within these ranges, the butyl rubber and parafiin are fully compatible and miscible with one another to provide uniform and stablemixtures.

The stability of themixture as made and as employed in coating metal, vinyl resin, chlorinated rubber, varnished paper, etc, webs and sheets, or other articles, such as the aluminum foil used above for the spots, is striking in comparison with apparent equivalents. Thus, mixtures of parafiin wax with natural or-buna rubbers, latex, etc., have a shelf life of a few days, after which the mixture is not competent of producing a tacky surface upon the normal heating or does not upon later cooling afiord a strong and permanent bond. some of thesynthetic rubbers, such as chlorinated butadiene elastomers, reject parafiin orpetroleum wax and give no tacky product at all. On the contrary, the present-mixtures can be subjected to repeated cycles of heating to tackiness or fusion andthen of cooling to surface hardness, Without losing the desirable properties of thermo-adhesivenes upon heating and strength while cooled to 32 degrees F. and below.

The other forms of butyl rubber in commerce can be used; for example, mixtures with GR-VI-AO are more tacky at any given temperature than those with (Eth l-60, but are less viscous at room temperatures so that they may be extruded from between a foil spot and'th'e cushion, while cap ping. a bottlecf warm liquid, and thus cause'unr desirable adhesionloetween the glass and, cork outside the area of the spot, but this very characteristic is of value where such adhesion is sought as a means of providing a secondary liquid and moisture-proof seal at such point. Butyl rubber has been defined by trade specifications such as those of the Committee on Specifications for Synthetic Rubbers of Rubber Reserve Company. GR-I is a standard product having a Mooney viscosity value between 40 and 50. Special grades are available: thus, GR-I-4O has a Mooney viscosity between 30 and 40, while GR-I-GO has a Mooney viscosity between 50 and 60. It is preferred to employ butyl rubber having a viscosity within the limits of substantially 30 to 70. Low viscosities have lower strength, while high viscosities are hard to work.

The preferred wax is a fully refined paraffin wax of about 132-135 degrees F. (American Melt ing Point), a specific gravity at 60 degrees F. (solid) of 0.889 and essentially of crystalline structure as distinguished from microcrystalline structure: and is available in commerce under such designation. The commercial product known as Atlantic Refining Company No. 171 has been found useful. The same companys No. 191" with a melting point of about 138-140 degrees F. is also satisfactory, while requiring a slightly higher temperature in use. These give a product which is non-tacky at normal room temperatures, and has a relatively sharp softening point so that the mass loses its tackiness rapidly during its cooling from high temperature, and thus quickly produces a stable bond. In general, the parafiin should be waxy at room temperature (e. g. 80 degrees F.); should soften at a temperature well below that at which the butyl rubber is damaged, preferably below a temperature of around 150 degrees F. so that water bath or low steam pressure conditions can be employed in spreading the mixture; should be well compatible with the butyl rubber; and preferably should be of comparatively high tensile strength (e. g. Atlantic No. 171 has a tensile strength of 300 p. s. i.).

It is at times desirable to add a material to reduce the surface-tack of the cooled material and to improve the adhesion effected while hot: that is, to prevent adhesion by the exposed surface of the mixture after the latter has been applied to foil and cooled, so that the turns of the wound coil will not stick together or block while it is being unwound during employment. An addition up to percent of a non-heat-hardening resin compatible with the butyl rubber and the paraffin, such as thermoplastic hydrocarbon resins of the olefin, diolefin, cyclopentadiene, styrene, and cumarone-indene types, having long aliphatic chains, is effective for this, A presently preferred resin, when such addition is de sired, is a mixture of polymers having a wide range of molecular weights and produced from crude mixtures of styrene and styrene homologs such as those obtained from the fractionation of so-called Crude Solvent from the light oils scrubbed out of coke oven or gas house gas; specifically, a useful mixture of such polymers is a soft solid at room temperature and demonstrates a slick waxy feeling at the undisturbed surface at room temperature, but exhibits stickiness when the mass is disturbed. This preferred styrene resin mixture is permanently thermoplastic, melts with essential sharpness at about 50 degrees C., and is heat-stable up to 175 degrees C. or above. It is compatible up to equal parts with paraffin wax and oil and in essentially any proportion with the rubber. These styrene resins are commercially available, and the material sold as Piccolastic A-50 is satisfactory. This effect can also be gained by including up to a like percentage of natural rubber, which leads to a slight surface oxidation that acts to prevent blocking.

A general characteristic of the adhesive is that it remains essentially non-tacky for a long time provided that it is kept at below about degrees F., and can be utilized by simple heating, being self-healing under such conditions; spots of foil having the adhesive thereon can be applied to cork cushions and primary adhesion obtained by low heating before further heating to essential fusion is used to seal and assure maximum strength. The self-healing and tasteless behavior assures that the seal will be essentially maintained during the minor distortions and weakenings of the foil produced during the capping operations.

The shelf life of the mixture permits the coating of film at a central plant and its shipment under ordinary temperature conditions to the spotting plant; and the storage of a large stockpile of coated film.

The aluminum foil is an illustrative example of a film material of limited permeability for liquids and vapors, and the composition cork disk is an example of a cellulosic cushion material. Obviously, as indicated, other materials may be substituted as a base, and such materials adhered to metal, or to the cellulosic surfaces of cork, paper, wood, etc., by the heating operations.

It is obvious that the invention is not restricted to the illustrative forms of practice, but that the same may be employed in many ways within the scope of the appended claims.

What is claimed is:

l. A composition capable of exhibiting tackiness upon each heating during repeated cycles of heating above and cooling below room temperature, and having the property of strong adhesion to metal and cellulosic surfaces after cooling in contact therewith, consisting of 40 to 50 parts by weight of paraffin wax having a melting point between 80 and 150 degrees F., and 60 to 50 parts by weight of a butyl rubber produced by low-temperature catalytic polymerizing combination of isobutylene with a substance selected from the group consisting of butadiene and isoprene, said butyl rubber having a Mooney viscosity of 30 to 70, the said ingredients being intimately and uniformly mixed.

2. A closure liner material comprising a film of material of limited permeability and on a face thereof a thermo-adhe'sive coating of a cement consisting of 40 to 50 parts by weight of parafiin wax with a softening point of substantially 132 to 135 degrees F., and 60 to 50 parts by weight of a butyl rubber produced by low-temperature catalytic polymerizing combination of isobutylene with a substance selected from the group consisting of butadiene and isoprene, said butyl rubber having a Mooney viscosity of 30 to 70, the said ingredients being intimately and uniformly mixed, said coating having a thickness of substantially three to four thousandths of an inch.

LOUIS F. ROGERS. MICHAEL S. EBERT.

(References on following page) 5' 5 6 Th 1 n f SQ S d i th FOREIGN PATENTS' me 5, 5 5 5; e are 0 w 8 Number Country We TED TENT 112,875 Australia Apr. 24, 1941 Numb UNI PA 5 D t 5 OTHER REFERENCES er ame a e Page 1, Butyl Rubber, a, publication of Stance 2,227,516 Soanes Jan. 17, 1941 I Dlstnbutors, Inc., 26 Broadway, New York, New 2,275,814 Abrams et a1 Mar. 10, 1942 York. Received 1n Pat. Off. Lib. December 1942. 2,367,250 Warth et a1 Jan. 16, 1945. I d1 1 94 2 403 9 4 Eamon July 1 19 4 10 n a Rubber June 1 p 2,413,239 Mason Dec. 24, 1946 2,419,304 Warth et a1 Apr. 22, 1947 

1. A COMPOSITION CAPABLE OF EXHIBITING TACKINESS UPON EACH HEATING DURING REPEATED CYCLES OF HEATING ABOVE AND COOLING BELOW ROOM TEMPERATURE, AND HAVING THE PROPERTY OF STRONG ADHESION TO METAL AND CELLULOSIC SURFACES AFTER COOLING IN CONTACT THEREWITH, CONSISTING OF 40 TO 50 PARTS BY WEIGHT OF PARAFFIN WAX HAVING A MELTING POINT BETWEEN 80 AND 150 DEGREES F., AND 60 TO 50 PARTS BY WEIGHT OF A BUTYL RUBBER PRODUCED BY LOW-REMPERATURE CATALYTIC POLYMERIZING COMBINATION OF ISOBUTYLENE WITH A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF BUTADIENE AND ISOPRENE, SAID BUTYL RUBBER HAVING A MOONEY VISCOSITY OF 30 TO 70, THE SAID INGREDIENTS BEING INTIMATELY AN UNIFORMLY MIXED. 